This is a Saxonorité neck screw for saxophone. The material is brass, and the plating is PGP. It's for Cannonball saxophones. It can also be used on UNISON saxophones. It helps to focus the sound and makes it easier to play low notes. Shiba screws, which are very popular neck screws, are no longer available for Cannonball saxophones, so if you're looking for a screw for your Cannonball or UNISON saxophone, how about this one? I think it's a little too big for a soprano saxophone, so it's best used on alto to baritone saxophones. I used it on my baritone saxophone.